Features of synergism between mesenchymal stem cells and immunosuppressive drugs in a murine heart transplantation model

Abstract

Background

Mesenchymal stem cells (MSCs) can be used for immunomodulation therapy after solid organ transplantation. Here, we focus on the immunoregulatory potential of combination therapies of MSCs and classic pharmacotherapy to mediate acceptance of solid organ grafts.

Methods

To determine which drugs influence the immunosuppressive effect of MSCs, we assessed the interaction of MSCs and common clinical immunosuppresants (MMF, sirolimus [Srl], and ciclosporin A [CiA]) in a parent-into-F1 cell transfer model. In this model, the transfer of parental strain T cells into semi-allogeneic F1 recipients induces a graft-versus-host reaction (GvHR). Re-isolated CFSE-labelled T lymphocytes were analyzed by flow cytometry. These findings were compared to a fully allogeneic heart transplantation model.

Results

We found that MSC treatment alone had no significant effect on allograft survival of heterotopic heart grafts. However, MSCs combined with short-term mycophenolate mofetil (MMF) significantly prolonged graft survival. Quantitative analysis of three different MSC – drug combinations in the F1 model revealed, that only the MSC–MMF combination led to a super-additive immunosuppressive effect. We also investigated the effect of MMF and CiA on IFNγ production of stimulated lymphocytes and found that MMF left the expression of IFNγ unaffected, whereas CiA completely abolished the production of IFNγ.

Conclusion

Our data show that the type of concurrent immunosuppression strongly influences the immunosuppressive effect of MSC, most likely through differential secretion of IFNγ. A regimen combining MSCs and MMF was most immunosuppressive.

Introduction

Long-term acceptance of solid organ grafts can be achieved with reasonable clinical success using standard pharmacological immunosuppression [1], [2]. However, clinical allograft acceptance comes at a price, with the unwanted side effects of life-long drug-based immunosuppression significantly reducing the overall well-being of transplant patients [3]. To overcome this shortcoming of immunosuppressive pharmacotherapy, cellular immunotherapy has been investigated as a promising alternative [4], [5], [6], [7]. To modulate anti-donor reactivity in favour of graft acceptance, bone-marrow–derived leukocytes, mostly of donor-origin, have been used [5], [8], [9], [10], [11]. Although some progress has been made in this area, the need for toxic preconditioning before bone marrow transfer has hampered the broad use of hematopoietic stem cells in the field of organ transplantation.

One alternative to hematopoietic progenitors are bone-marrow-derived mesenchymal stem cells (MSCs). They represent an independent mesodermal stem cell lineage within the bone marrow compartment [12], [13], [14] and can easily be harvested and cultured from adult bone marrow and other organs of essentially any mammal [15]. The well-described ability of MSCs to suppress T-cell proliferation in culture has inspired investigations assessing the use of MSCs as immunotherapeutics [12], [16]. To date, most immunological studies have applied MSCs to patients with graft-versus-host disease (GvHD) [17], [18]. The effectiveness of MSCs in controlling GvHD has prompted us and others to compare the potential of MSCs (combined with short-term, reduced-intensity immunosuppression) to achieve graft acceptance of solid organ allografts to the results obtained in the GvHD studies. Current experimental studies suggest that MSCs can, under certain conditions, prolong allograft survival [19], [20], [21], [22] together with immunomodulatory drugs. Understanding the interaction between MSC and drugs in vivo is particularly important for the clinical setting. Specifically, MSC function has been shown to depend on the choice of concurrent immunosuppressants [23].

In this study, we sought to determine the effect of MSCs on T-cell proliferation in the presence of different immunosuppressive drugs using a fully allogeneic vascularized heart transplantation model and a murine parent-to-F1 adoptive lymphocyte transfer model. In the latter model, the transfer of homozygous parental-strain T cells into non-irradiated semi-allogeneic F1 recipients induces a graft-versus-host reaction (GvHR). It is therefore suitable to visualize alloproliferation (“in vivo MLR”).

We show that different immunosuppressive drugs significantly alter the tolerogenic effectiveness of MSCs and that the type of concurrent immunosuppression is crucial for MSC combination therapies in vivo.